Large Scale Gas Chromatography

capacity is enlarged (by increasing the diameter) and, at the column outlet, instead of discharging the various fractions to the atmosphere, they are directed to traps where they are condensed and separated from the carrier gas.

Two different categories of preparative GC exist which differ in both size and goal: laboratory-scale preparative GC and large scale preparative GC. Laboratory-scale preparative GC will not be described here since it is very similar to analytical GC. Its goal is to purify milligrams or hundreds of milligrams of compounds in order to identify them further: it is an analytical technique. The equipment used is similar to that used in analytical GC (except for column diameters that can be increased up to 10 mm) and the fraction collector is a simple device in which sample condensation is often not quantitative.

Large scale preparative GC, described below, is made for purification of kilograms and tonnage quantities of compounds.

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